1. Field of the Invention
The present invention relates to an optical disk, and more particularly relates to a rewritable optical disk having a control data signal representing the type of the disk and the like recorded thereon.
2. Description of the Related Art
In recent years, various types of optical disks, for example, read-only types such as a CD and a CD-ROM and types which allow for data recording such as a data addition type and a rewritable type, have been widely used. Some of such optical disks of the read-only type, the data addition type, and the rewritable type are the same in appearance and the like, though they are different in type from each other.
Some of the optical disks are different from others in format type and parameters to be set at recording and/or reproduction. Information on the format type and information for setting parameters is therefore prerecorded as control data signals in a predetermined region of the disk, so that the control data signals are read with a drive for reproducing/recording data from/on the optical disk before various parameters are set for the drive.
A method for recording such control data signals on an optical disk will be described, using a "130 mm rewritable optical disk" as an example.
The "130 mm rewritable optical disk" has a format defined by JIS X6271. Two types of formats are defined by the standard: i.e., Format A where continuous grooves are formed spirally on a disk, and lands between adjacent grooves are used as tracks for recording signals; and Format B where marks for sampling are formed on a disk to allow for tracking control by a sample servo method. The two formats are common in the configuration of a control information track where the control data signals are recorded. That is, the control information track is specified to have a PEP region, an inner SFP region, and an outer SFP region for the two formats.
The PEP region is located on the innermost portion of the disk, where prerecord marks (also called embossed pits), obtained by modulating with low-frequency phase-modulated recording codes, are used. All the marks in the PEP region are arranged so as to be aligned in the radial direction of the disk. This arrangement is schematically shown in FIG. 3A. Each prerecord mark and each space between adjacent prerecord marks are two channel bits long. One PEP bit cell has a length of 656.+-.1 channel bits. FIG. 4 shows forms of such PEP bit cells. The information of the PEP bit cell is represented by a phase-modulated recording code. A PEP bit cell where marks are formed in the first half thereof represents logical 0, while that where marks are formed in the second half thereof represents logical 1. A total of 561 to 567 PEP bit cells of the above forms per track are recorded on the disk.
The PEP region has a track format shown in FIG. 5A, which includes three sectors. FIG. 5B shows a sector format of each sector. The numbers shown in FIGS. 5A and 5B represent the numbers of PEP bit cells allocated to respective signals. A data region of the sector format where various control signals are recorded has a capacity of 18 bytes (144 PEP bit cells) (hereinafter, bytes are referred to as "B"). For example, a signal representing the format (Format A or B) to be used by the disk is recorded in byte 0. The details on other control signals to be recorded on the data region are specified in the aforementioned JIS standard. The description thereof is therefore omitted here.
When the PEP region with the above format is illuminated with light with an optical head or the like, light is focused on a signal recorded surface of the disk by focusing control. Since marks are aligned in the radial direction in the PEP area, signals can be reproduced without tracking control.
FIG. 3A also shows an example of a beam track. The portion where no marks are formed serves as a mirror, producing a large amount of reflection light. The portion where marks are formed diffracts reflection light depending on whether or not the marks exist at respective positions on the disk. Therefore, the average level of the amount of reflection light is low compared with that of the mirror portion.
FIG. 3B shows a change in amount of reflection light. Since the repetition frequency of the marks is higher than the period of the PEP bit cells, mark signal components can be eliminated by limiting the band for a reproduction signal. The waveform of the reproduction signal obtained by band limit is shown in FIG. 3C. The information of each PEP bit cell can be detected by examining the level of the reproduction signal.
Then, the inner and outer SFP regions of the control information track will be described. The same information is recorded in the inner and outer SFP regions. That is, prerecord marks are recorded in the inner and outer SFP regions under a standard user data format. A 512 B region is allocated for the control data signals. For example, the same information as the 18 B information recorded in the PEP regions is recorded in bytes 0 to 17. The details on other control information to be recorded in this region are specified in the aforementioned JIS standard. The description thereof is therefore omitted here.
FIG. 6 shows an example of the standard user data format of each sector where the user data capacity is 512 B and Format A is used. The numbers shown in FIG. 6 represent the numbers of bytes (B) allocated to respective signals. The capacity of the data region becomes 650 B including an error correction code, re-synchronization bytes, and control bytes in addition to the 512 B user bytes.
This sector for recording signals in the data region also includes the following regions: a prerecorded address section composed of a sector mark (SM) indicating the head of the sector, a VFO region for synchronizing clock reproduction, an ID region indicating the address of the sector, an address mark (AM) indicating the head of the ID region, and the like; and regions for rewriting data, such as an offset detection region (ODF), an ALPC used for detection of laser output, and a buffer region provided to avoid overlap with a subsequent sector.
The total capacity of the sector is therefore 746 B. Although the control data recorded in the SFP regions are prerecord marks, the capacity of 746 B is required to record the 512 B control signals, as in the case of recording user data, since the control data is recorded under the user data format.
In recent years, read-only optical disks in which digitized and compressed image and sound signals are recorded have been proposed. FIGS. 7A to 7C show an example of a sector format of one of such read-only optical disks called a DVD (digital video disk).
A 2048 B unit of information data such as image and sound is recorded in one sector. This unit is called a first data signal. The sector also includes a 4 B data ID, a 2 B IED for error detection of the data ID, a 6 B RSV as reservation, and a 4 B EDC for error detection of the entire sector. Such one sector including these regions is called a first data unit. FIG. 7A shows a configuration of the first data unit which has a data length of 2048+4+2+6+4=2064 (B).
The information data (2048 B) is scrambled in the following manner. A shift register is constructed so that so-called M-series data is generated. An initial value is set for the shift register, and is sequentially shifted in synchronization with the data, so as to generate pseudorandom data. An exclusive-OR between the generated pseudorandom data and the information data to be recorded is calculated every bit. Thus, the information data (2048 B) is scrambled.
A total of 16 sectors of the thus-scrambled first data units are put together to constitute an error correction code of Reed Solomon coding. In such an error correction code, each data unit constituting one sector is arranged in an array of 172 B.times.12 rows and a total of 16 sectors of such data units are put together to constitute an array of 172 B.times.192 rows. A 16 B outer code is added to each column of the array, and then a 10 B inner code is added to each row of the resultant array. As a result, as shown in FIG. 7B, a data block of 182 B.times.208 rows (37856 B) is formed. This data block is called an ECC block.
The ECC block is then interleaved so that the 16 B outer codes are included in the respective sectors. Thus, the data capacity of each sector becomes 182 B.times.13 rows=2366 B.
The resultant data is then modulated with a recording code. A RLL (run length limited) code where the run length after modulation is limited is used as the recording code. As an example, a 8/16 conversion code which converts 8-bit data into 16-channel-bit data is used. This conversion is conducted based on a predetermined conversion table. According to this conversion, DC components included in the recording code can be suppressed by controlling the code selection, though the detailed description of this control is omitted here.
In this modulation, the minimum and maximum bit lengths are limited to 3 and 11 channel bits, respectively. In order to secure synchronization at reproduction, a 2 B synchronization code is inserted every 91 B, i.e., a half of one row of 182 B. As the synchronization code, several different codes with a length of 32 channel bits having patterns which normally do not appear in the 8/16 conversion code are predetermined. This period of 93 B data including the synchronization code is called a frame. This configuration is shown in FIG. 7C. Thus, the data capacity of each sector is now 186 B.times.13 rows=2418 B.
In a read-only DVD having a single signal recording surface, data is recorded by forming pits on the disk from the inner circumference thereof toward the outer circumference at a constant linear velocity (i.e., by CLV driving) in accordance with the above-described sector format. A read-only DVD having double signal recording surfaces has also been proposed, though the description of data recording on such a disk is omitted here.
FIG. 8 shows a configuration of signal recording areas of the read-only DVD. A lead-in area is located on the innermost portion of the disk, which starts at a diameter of 22.6 mm. A data area where information data such as image and sound is recorded starts at a diameter of 24.0 mm and ends at a diameter of 58.0 mm at maximum. A lead-out area follows the data area and ends at a diameter of 58.5 mm at maximum. The sector address is 30000 in the hexadecimal notation (denoted as 30000h) at the head of the data area, and increases by 1h every sector toward the outer circumference of the disk. In the lead-in area, the sector address decreases by 1h every sector toward the inner circumference of the disk.
The control information is recorded in the lead-in area under the sector format described above. In the lead-in area, a reference code which is used for identification of the disk manufacturer, reproduction adjustment, and the like is recorded over two ECC blocks covering sector addresses starting from 2F000h to 2F020h. The control data is recorded over 192 blocks covering sector addresses from 2F200h to 2FE00h. In the other sectors in the lead-in area, information data is recorded as 00h under the sector format described above.
A rewritable DVD which is compatible in format with the above-described read-only DVD has been proposed. In such a rewritable optical disk, spiral or concentric grooves are formed on a disk substrate, and a recording film is formed on the substrate to define tracks along the grooves. In order to maximize the recording capacity, both grooves and lands between adjacent grooves are used as recording tracks.
Each track is divided into a plurality of sectors as units for data recording and reproduction. Address information is added to each sector so that the position of required information data can be managed to facilitate high-speed data retrieval. More specifically, a header region which includes an ID signal representing the address information of the sector is provided at the head of the sector.
In order to secure the compatibility with the read-only DVD, the rewritable DVD has a format so that the 2418 B data of one sector of the read-only DVD can be recorded in a user data region of one sector of the rewritable DVD as a unit. This 2418 B data is called a second data signal.
The sector format for the rewritable DVD also requires an ID region indicating the address number of the sector and a buffer region, as in the case of the optical disk according to the aforementioned JIS standard. The total capacity of the sector including these regions is preferably a multiple of the frame length (93 B) of the format for the read-only disk.
FIG. 9 shows an example of the format for the rewritable DVD which satisfies the above requirements. The 2048 B data (first data signal) is arranged under a format similar to that used for the read-only DVD described above, to obtain 2418 B data (second data signal), and the resultant 2418 B data is recorded in a data region 91 shown in FIG. 9. A 1 byte postamble (PA) region 92 follows the data region 91. In the case of the 8/16 conversion code, the end of the recording code should be identified so that the converted data can be correctly decoded. The PA is provided to identify the end of the recording code, and a pattern obtained by modulating a predetermined code in accordance with a modulation rule is recorded.
A PS region 93 precedes the data region 91, where a presync signal is recorded to indicate the start of the data region and obtain byte synchronization. As the presync signal, a code with a length of 3 B (48 channel bits) which has high autocorrelation is predetermined. A VFO region 94 precedes the PS region 93, where a signal with a specific pattern is recorded to obtain prompt and stable clocking of a PLL (phase-locked loop) of a reproduction circuit.
The specific pattern of the signal is, for example, a repetition of a 4-channel-bit pattern, i.e., ". . . 1000 1000 . . . " as represented in NRZI coding. The length of the VFO region 94 is 35 B to secure the frequency of the inversion and the duration required for stable clocking.
A first guard data region 95 precedes the VFO region 94, while a second guard data region 96 follows the PA region 92. In a rewritable recording medium, the head and end portions of the recording area thereof degrade after repeated recording and deletion. The guard data regions 95 and 96 are therefore required to have a length large enough to prevent the degradation from affecting the area from the VFO region 94 to the PA region 92. It has been found from experiments that the lengths of the first and second guard data regions 95 and 96 should be 15 B and 45 B, respectively. Data to be recorded in these guard data regions are, for example, the same repetition of the 4-channel-bit pattern as that used for the VFO region 94, i.e., ". . . 1000 1000 . . . ".
A gap region 97 is provided for setting a laser power. The length of the gap region 97 is 10 B to secure the time required for the setting of the laser power. A buffer region 98 is provided to secure a time width where no data is recorded to ensure that the end of the recording data does not overlap a subsequent sector even if a variation in rotation of a disk motor or disk eccentricity occurs. The length of the buffer region 98 is 40 B.
The above regions 91 to 98 constitute an area where rewritable data is recorded and has a total length of 2567 B. The signal recorded in this area is called a third data signal.
A 2 B mirror region 99 is provided to secure the time required for determining an offset of the servo tracking.
Next, a header region 100 will be described. As shown in FIG. 9, a first half 19 and a second half 20 of the header region 100 are displaced from the center line of the groove in the opposite radial directions from each other by about a quarter of the pitch of the groove, so that the header region can be read from both the groove track and the land track. The header region 100 includes total four sector ID signals (PIDs). For the groove track, for example, sector ID signals PID1 and PID2 in the first half 19 are displaced toward the outer circumference of the disk, while sector ID signals PID3 and PID4 in the second half 20 are displaced toward the inner circumference of the disk.
A 4 B Pid region representing the address information of the sector is provided in each sector ID signal PID. In the Pid region, 3 B is allocated for the sector number and the remaining 1 byte is allocated for various types of information such as the PID number. In a Pid3 region 113 and a Pid4 region 118, the address information of the sector on the groove track having the center line from which the PIDs are displaced is recorded. In a Pid1 region 103 and a Pid2 region 108, the address information of the sector on the land track adjacent to the groove track on the inner side thereof is recorded. IED regions 104, 109, 114, and 119 with a length of 2 B represent an error detection code for the preceding respective Pid regions. The data in the Pid regions and the IED regions are modulated with the 8/16 conversion code described above. In order to identify the end of the conversion code, 1 byte postamble (PA) regions 105, 110, 115, and 120 are provided.
AM regions 102, 107, 112, and 117 precede the respective Pid regions, where address mark signals are recorded to indicate the start of the Pid regions and obtain byte synchronization. Each address mark signal has a length of 3 B (48 channel bits), and a code having a pattern which does not appear in the 8/16 conversion code is predetermined.
First and second VFO regions 101, 111, 106, and 116 are provided at the heads of the respective PIDs. As in the VFO region 94, the repetition of the 4-channel-bit pattern, ". . . 1000 1000 . . . " is used for these VFO regions. In the header region 100, the first half including the sector ID signals PID1 and PID2 and the second half including the sector ID signals PID3 and PID4 are displaced in the opposite radial directions as described above. Accordingly, in order to resume the bit synchronization, the first VFO regions 101 and 111 located at the heads of the first and second halves of the header region 100 are made long. On the contrary, the second VFO regions 106 and 116 of the first and second halves may be short since they are only required for re-synchronization. For example, the lengths of the first and second VFO regions are 36 B and 8 B, respectively.
As a result, the total length of one sector of the rewritable DVD is 2697 B. Thus, the length of one sector of the rewritable DVD is larger than that of one sector of the read-only DVD by 279 B (corresponding to three frames).
As described above, in the rewritable DVD, as in the read-only DVD, it is necessary to prerecord the control data signals indicating various types of control information. This can be performed using the prerecord marks, as in the case of the above-described "130 mm rewritable optical disk", under the sector format used for the "130 mm rewritable optical disk". The length of one sector of the rewritable DVD is larger than that of one sector of the read-only DVD by about 10% or more as described above. Since the control data signals are recorded at the fabrication of the disk and will not be rewritten, this increase in the sector length is unnecessary for the recording of the control data signals. This unnecessary increase in sector length is therefore disadvantageous for DVDs which are demanded to have a large capacity.
A drive for DVD disks is required to be able to record and/or reproduce both read-only DVDs and rewritable DVDs. However, the read-only DVDs and the rewritable DVDs are different in sector format. The type of the disk mounted in the drive can be identified by reading the control data signal. However, in order to read the control data signal, the format of the disk must be identified to locate the recorded position of the control data signal.
In order to identify the type of the disk, a region with the same sector format may be set for both the read-only type and the rewritable type using rerecord marks so as to record a signal indicating the type of the disk in the region, as in the case of the PEP region of the above-described "130 mm rewritable optical disk". This common region is first reproduced at the activation of the disk to identify the type of the disk. Once the type of disk is identified, the control data on the disk can be reproduced in accordance with the format for the disk. However, as in the case of the "130 mm rewritable optical disk", the signal indicating the type of the disk recorded on the common area is the signal recorded as part of the control data signal. Recording the same control data signal on two different regions results in redundancy of the recording area. The redundancy of the recording area is disadvantageous for DVDs which are demanded to have a large capacity.
In view of the foregoing, the objective of the present invention is to provide an optical disk in which control data signals are recorded under a format which can be easily read regardless of the type of the optical disk, a read-only DVD or a rewritable DVD, and redundancy is reduced to improve the recording capacity.